This application is related to and claims priority from Japanese Patent Applications No. Hei. 11-244460 filed on Aug. 31, 199, No. Hei. 11-247912 filed on Sep. 1, 1999 and No. Hei. 11-252929 filed on Sep. 7, 1999, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a cooling device for cooling a heat-generating member by boiling and condensing refrigerant.
2. Description of Related Art
In a conventional cooling device for cooling a heat-generating member such as an electronic component, refrigerant in a refrigerant tank is boiled by heat from the heat-generating member, and gas refrigerant from the refrigerant tank is condensed in a radiator. For reducing a sealed amount of expensive refrigerant, the refrigerant tank is formed to be thinned. However, when an evaporated amount of refrigerant within the refrigerant tank increases, i.e., when a heat-generating density becomes larger, a temperature of a boiling surface of the refrigerant tank rapidly increases so that liquid refrigerant may be dried out.
On the other hand, in a cooling device boiling and condensing refrigerant described in JP-A-10-209355, JP-A-10-209356 or JP-A-11-87583, a heat-generating member (e.g., CPU) is fixed to a heat-receiving wall of a flat-box type refrigerant tank in which a predetermined amount refrigerant is sealed, and a radiator fin is attached to a heat-radiating wall of the refrigerant tank, opposite to the heat-receiving wall. In the cooling device, heat generated from the heat-generating member is transmitted to refrigerant within the refrigerant tank through the heat-receiving wall so that refrigerant is evaporated, and the evaporated gas refrigerant is cooled and condensed in the heat-radiating wall so that condensation latent heat of refrigerant is transmitted to an outside fluid through the heat-radiating wall. However, in this case, when pressure of the sealed refrigerant becomes higher and a distortion is caused due to the pressure in the refrigerant tank, the heat-generating member does not sufficiently contact the refrigerant tank. Therefore, heat-transmitting performance between the heat-generating member and the heat-receiving wall of the refrigerant tank becomes insufficient, and the heat-generating member is not sufficiently cooled.
In view of the foregoing problems, it is an object of the present invention to provide a cooling device boiling and condensing refrigerant, which prevents refrigerant from being dried out on a boiling surface of a refrigerant tank even when a gas-refrigerant generating amount becomes larger.
It is an another object of the present invention to provide a cooling device boiling and condensing refrigerant, which improves heat-transmitting performance from a wall part of a refrigerant tank to refrigerant, with a simple structure.
It is a further another object of the present invention to provide a cooling device having first and second radiator portions, which improves heat-radiating capacity in a downstream radiator portion among the first and second radiator portions, disposed at a downstream side relative to a flow direction of outside fluid.
According to a first aspect of the present invention, a cooling device boiling and condensing refrigerant includes a refrigerant tank for defining a refrigerant chamber in which liquid refrigerant is stored and a part of liquid refrigerant is boiled and vaporized by absorbing heat from a heat-generating member attached onto one side wall part of the refrigerant tank, and a radiator disposed on the other side wall part of the refrigerant tank to perform a heat exchange between gas refrigerant from the refrigerant tank and outside fluid passing through the radiator. The refrigerant tank has therein a plurality of refrigerant passages continuously extending in an up-down direction at least in a range of a boiling surface of the refrigerant tank, and each passage width of the refrigerant passages is set to be equal to or smaller than double Laplace length. Thus, bubble dimension of gas refrigerant boiled in the refrigerant chamber by heat from the heat-generating member becomes larger than a passage width of the refrigerant passages; and therefore, liquid refrigerant rises in the refrigerant chamber when bubbles of gas refrigerant move upwardly in the refrigerant passages. Accordingly, even when gas-generating amount is increased, liquid refrigerant can be supplied to the boiling surface of the refrigerant chamber while it can restrict liquid refrigerant surface from being lowered.
According to a second aspect of the present invention, a porous layer made of a material having a sufficient heat conductivity is disposed on an inner surface of the one side wall part, defining the refrigerant chamber, at least in a part of the inner surface opposite to the heat-generating member. Therefore, a contact area of the refrigerant tank with refrigerant is increased by the porous layer, and refrigerant is readily evaporated by the porous layer. That is, heat-transmitting performance from the one side wall part to refrigerant is improved by the porous layer. Thus, refrigerant can be effectively evaporated in a wide range of the refrigerant tank, and super-heating degree of refrigerant around a position where the heat-generating member is disposed can be reduced.
According to a third aspect of the present invention, the radiator includes a first radiator portion for performing heat exchange between gas refrigerant from the refrigerant tank and outside fluid passing through the first radiator portion, and a second radiator portion for performing heat exchange between refrigerant from the first radiator portion and outside fluid passing through the second radiator portion. The second radiator portion is disposed at a lower side of the first radiator portion in an up-down direction. A duct extending in the up-down direction is disposed to enclose both the first radiator portion and the second radiator portion, to define an outside fluid passage through which outside fluid passes through both the first radiator portion and the second radiator portion in the up-down direction. One upstream radiator portion among the first radiator portion and the second radiator portion, disposed at an upstream side relative to a flow direction of outside fluid, is disposed to be separated from an inner surface of the duct so that a clearance through which outside fluid bypasses the upstream radiator portion is defined between the inner surface of the duct and the upstream radiator portion. Thus, low-temperature outside fluid passing through the clearance can be supplied to the other downstream radiator portion among the first and second radiator portions, disposed at a downstream side relative to the flow direction of outside fluid. As a result, heat-radiating capacity of the downstream radiator portion can be improved.